The present invention relates to a probe needle, and a method of coating a probe needle.
Conventionally, following the fabrication of a semiconductor device element such as an LSI, IC chip or the like on a semiconductor wafer (hereinafter referred to simply as "wafer") that has been subjected to wafer processing, the quality of each chip is determined by performing tests of the electrical characteristics during a process that is called probe testing, using a test apparatus called a prober, in order to check for various faults such as short-circuits or open-circuits in the pattern, or the characteristics of the chips.
The wafer is subsequently separated into individual chips, the chips that have passed the above tests are packaged then subjected to further predetermined testing, and the final products are shipped after their quality has been determined.
During the checking of electrical characteristics by these probe tests while the wafer is still in wafer form, the wafer is mounted on a mounting stand, then measurement pads on the wafer are brought into electrical contact with, for example, probe needles or bumps made of tungsten (W) that are arranged in a probe card provided in the probe device. Further, a predetermined test signal is sent for each chip by bringing the above probe card into electrical connect with a test head via a contact ring, and the testing is implemented by monitoring the resultant responses.
However, prior art contactors are not provided with any particular countermeasures against noise, and thus when such prior art contactors are used for measuring an object under test that requires high-frequency testing, for example, a problem is encountered in that reliable measurement is prevented by noise and crosstalk between signal channels.
Recently, as semiconductor devices have become more densely integrated, the pitch of the measurement pads on each semiconductor chip has become tighter, and thus it is becoming necessary to arrange the tips of the probe needles used by the probe tests at a correspondingly tighter pitch.
In other words, when probe needles are arranged in a prior art probe card, they are arrayed in such as manner that adjacent probe needles in each group do not touch each other, and the groups of probe needles are fixed by epoxy resin in such a manner that they are held in position. However, there are limitations on the tightness of pitch possible with a configuration where groups of probe needles are not permitted to touch.
This problem will now be described in further detail with reference to a probe device using vertically aligned needles, as shown in FIG. 15A and FIG. 15B.
As shown in FIG. 15A, the probe device using vertical needles is provided with conductive probe needles 4 that are set up vertically between a fixed plate 7 and guide plates 2 and 3. The configuration of the probe needles 4 is such that upper ends thereof are fixed at predetermined positions on a printed circuit board 5, and also lower ends thereof are in electrical contact with measurement pads 8 on a semiconductor chip W that is mounted on a mounting stand 6. The probe needles 4 are also fixed between the fixed plate 7 and the printed circuit board 5 by means such as a plug of epoxy resin 9.
During the measurement, the intention is to ensure electrical conduction between the measurement pads 8 and the tips of the probe needles 4 by moving the mounting stand 6 through a very small distance .delta.Z in the Z-axis direction, as shown in FIG. 15B. In this case, the parts of the probe needles 4 between the guide plate 2 and the fixed plate 7 deform slightly to absorb motion in the vertical direction. However, if the probe needles 4 are set at a tight pitch, it is possible that groups of adjacent probe needles 4 will touch each other, as shown at reference symbol D, causing short-circuits.
Note that FIG. 15A and FIG. 15B illustrate an example of vertically aligned probe needles, but the same problem can occur with horizontally aligned probe needles where the probe needles are arrayed horizontally, in that, if the tightness of pitch is increased, groups of adjacent probe needles could bend and touch each other, causing short-circuits.
Another problem concerns the way in which it is currently unavoidable to rely on manual work to insert the probe needles into the probe card. Thus it is possible that groups of adjacent probe needles will touch and cause short-circuits during the fabrication and assembly, and so countermeasures are required.
For the above described reasons, there is a strong demand for covering the entire probe needle, except for parts such as the tip thereof, with an electrically insulating film or a protective film. Thus, various techniques have been proposed for providing an insulating coating over the probe needle, such as by placing an insulating sleeve over the probe needle, or painting an insulating agent thereover, and by further forming a thin, pinhole-free, uniform film of a material such as poly-para-xylene thereover by vacuum deposition.
Of these various coating techniques, methods of forming coatings of insulating or conductive films by vacuum deposition that have been developed by the present inventors are attracting attention because of the simplicity of such processing and the high quality of the finished product. However, when coating is done by such vacuum deposition, there still remains a problem concerning how to mask portions where coating is not required (non-coating portions), such as the tips of the needles.
Methods using masking tape or a masking rubber that has a volatile fixative have been considered as methods of masking the non-coating portions. However, each of these methods results in problems such as deformation of the extremely fine probe needles by adhesives or by hardening contraction, and accurate masking boundaries cannot be obtained because of spreading of the masking agent.